Saturday, 23 July 2011

Digging over the pea bed

I don't usually dig in July and this is probably the first year that I have done just that. Due to lack of time the ground is usually just hoed then cultivated using the three pronged cultivating tool and finally raked. This will prepare the ground for replanting. However, this year I am digging.

The reason why I am digging the ground this year is to incorporate the tops of the old pea plants into the soil. Peas and beans will add extra nitrogen but only if the old plants are allowed to rot down in the soil. Nitrogen from the atmosphere is captured by Rhizobium bacteria in nodules on the pea and bean root. Some of this nitrogen is transferred to the pea or bean plant in exchange for carbohydrates produced during photosynthesis by the plant.
The nitrogen is used by the plant to make proteins - vital building blocks of cells. This means that there is a net gain in organic nitrogen.

This nitrogen will only be released to the soil when the plant begins to decompose. It has been said that you should leave the roots in the soil, cutting the tops off and burning or composting the them. Only 30% of the captured nitrogen is in the roots while 60% is in the tops. If you cut up and bury the tops as well you will be adding 90% of the captured nitrogen to the soil.

So this is why I am digging in July. It is hot work and if it was not cold and rainy I don't think I would be inclined to spend so much energy digging trenches. It did not take very much time to bury the pea plants so I needed to fill the other trenches with different green manure. I scouted around the allotment for anything that needed to be composted or buried. The lettuce had gone over and started to rot so they went in the trench. There was nothing else that needed to be buried.

The raspberries have gone over now and I will have to cut out the fruiting canes. These are woody and will not rot down very quickly in the soil. However, I will still put them at the bottom of the trenches.

I am filling the trenches with grass mowings from the bays by the entrance gates. There is a great deal of nitrogen locked up in grass mowings. It is not nitrogen that has been captured by Rhizobium bacteria but it could be nitrogen captured by Azotobacter, free living nitrogen fixing bacteria. Grass has a NPK ratio of 1.0:0:1.2. and this is good enough for me.

The grass mowings were very hot when I was collecting them from the bays. Whether this will affect the new pea plants when I put them in remains to be seen. I would conjecture that it will not affect them at all.

Under the first spit of soil the ground was very dry. I was quite surprised because of the amount of rain we have been having. Not as much as I thought by the looks of things. Adding more organic matter to the soil will help it retain water and improve the drainage at the same time.

I podded the peas when it was raining but I still have quite a few to pod tomorrow. I will harvest quite a few things tomorrow. These will include salsify, scorzonera, beetroot, carrots, rainbow chard, rhubarb, potatoes, tomatoes, lettuce, turnip, blackberries, raspberries and podded peas.